Forward in situ combustion method for reocvering hydrocarbons with production well cooling



Il-A|R Oct. 22, 1968 L. G. SHARP 3,406,755

FORWARD IN SITU COMBUSTION METHOD FOR RECOVERING HYDROCARBO WITHPRODUCTION WELL COOLING iled May 31, 1967 PRODUCTION 34 WATER 24 v 4FUEL INVENTOR LORLD 6. SHARP ATTORNEY United States Patent FORWARD INSITU COMBUSTION METHOD FOR RECOVERING HYDROCARBONS WITH PRODUC- TIONWELL COOLING Lorld G. Sharp, Irving, Tex., assignor to Mobil OilCorporation, a corporation of New York Filed May 31, 1967, Ser. No.642,561 5 Claims. (Cl. 166-41) ABSTRACT OF THE DISQLOSURE A method forthe recovery of hydrocarbons, by forward in situ combustion, from asubterranean formation employing production well cooling. Morearticular- 1y, an in situ combustion front is moved by the injection ofoxygen-containing gas into the formation through an injection welltoward a spaced production well. The front displacescombustion-generated heated fluids, and formation fluid containingcombustible hydrocarbons, into the production well. These fluids areproduced from the production well and hydrocarbons recovered from them.Eventually, the combustion front moves sufliciently close to theproduction well to create temperatures therein at which combustion andthermal destruction of the desired hydrocarbons can occur. In accordancewith this invention, water is passed from the well into the surroundingformation at an upper horizon, then downward about the production wellto a lower horizon where the water is coproduced into the productionwell with fluids displaced before the combustion front. The combustionfront approaches the production well between the mentioned upper andlower horizons. The flow of water maintains temperatures within theproduction well above about 160 F. and below the temperature whereincoking of the produced hydrocarbons occurs. In a preferred aspect, atleast a part of the water produced into the production well is in theform of steam.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the recovery of hydrocarbons from subterranean carbonaceousformations. More particularly, it relates to a method for the recoveryof hydrocarbons from subterranean formations employing forward in situcombustion.

Description of the prior art The use of forward in situ combustionprocedures for the recovery of hydrocarbons from a subterraneancarbonaceous formation has been practiced in the oil industry. In theseprocedures, combustion is initiated in the carbonaceous material presentwithin the formation, and then is maintained by a flow of anoxygen-containing gas between injection and production wells. Theresulting combustion front is moved through the formation toward theproduction well. The combustion front may be described as a forwardcombustion front. Similarly, the procedure using this front forrecovering hydrocarbons is generally known as forward in situcombustion. The combustion front displaces combustion-produced heatedfluids, and formation fluid which includes combustible hydrocarbons,into the production well. The desired hydrocarbons are recovered fromthese fluids. The temperatures generated at the combustion front may beas high as 2500 F. Usually, fluid temperatures downstream of the frontaverage about 1000 F. It will be apparent that, with the front close tothe production well, these temperatures are sufficient to cause coking,and even combustion, of the produced hydrocarbons in the pro 3,406,755Patented Oct. 22, 1968 duction well, and also thermal destruction ofdownhole well apparatus.

There have been several proposals for overcoming these difiiculties inthe production well caused by the heated fluids generated by thecombustion front, and the destructive temperatures which can beproduced, by their flow, into the production well. For example, onemethod, of considerable usefulness, is described in US. Patent3,259,185. Other procedures are described in Us. Patents 2,994,375,3,013,609, 3,227,215, 3,228,471 and 3,240,270. Although the proceduresdescribed in these patents may be employed to prevent destructivetemperatures generated by a closely adjacent combustion front, fromoccurring within the production well, they all use the production wellas a heat exchanger.

More particularly, the procedures of these patents require that acooling fluid is circulated through the production well to preventoccurrence of undesired temperature effects therein. It will be readilyseen, in these procedures, that the production well serves as a heatexchanger. Should the flow of the cooling fluid suffer maladjustment inrate of flow, destructive temperatures can be quickly reached within theproduction well causing thermal destruction therein to well apparatusand produced hydrocarbons. Cooling of the production well by some meansis necessary when hydrocarbons are produced from a formation by anadjacent in situ combustion front. The method of the present invention,in recovering hydrocarbons by forward in situ combustion, provides forcooling of the production well but without using the production wellheat exchanger.

SUMMARY OF THE INVENTION The present method is an improvement to amethod for recovering hydrocarbons from a subterranean carbonaceousformation wherein combustion of combustible materials in the formationhas been initiated. A flow of oxygen-containing gas through theformation between spaced-apart injection and production wells maintainscombustion to produce a forward in situ combustion front which movestoward the production well. The front displaces combustion-producedheated fluids, and formation fluid containing combustible hydrocarbons,into the production well. Hydrocarbons are recovered from these fluids.More particularly, the present invention provides an improvement in thismethod, which comprises practicing the steps of:

(a) passing water from the production well into the surroundingformation at an upper horizon, then downward through the formation aboutthe production well to a lower horizon, and then back into theproduction well from the surrounding formation at the lower horizon, thehorizon at which the combustion front approaches the production wellbeing intermediate the upper and lower horizons,

(b) controlling the rate of water flow so that the Water enters theproduction well in amounts sufficient to maintain therein a temperaturebetween about 1-60 F. and the coking temperature of the hydrocarbons ata time when the combustion front is sufliciently close to the productionwell to cause increased temperatures in the production well, and

(c) producing the displaced formation fluid, heated fluids from thecombustion front, and the mentioned water, from the lower horizon of thesurrounding formation via the production well, and recoveringhydrocarbons from the produced fluids.

In further improvement, the rate of water flow may be controlled tomaintain the water entering the production well at least in part assteam. The rate of water flow may be arranged so that the temperatures,within the well, are maintained between the steam-water equilibriumtemperature and the coking temperature of the hydrocarbons flowingthrough the production well. Other arrangements of steps may be taken aswill be apparent from the following description of the present method.

DESCRIPTION OF THE DRAWING The drawing shows, in a vertical sectiontaken through the earth, a subterranean carbonaceous formation in whichforward in situ combustion is practiced according to the presentinvention for the recovery of hydrocarbons. Suitable apparatus isillustrated for carrying out the steps of the present method.Additionally, several results of practicing the steps of this method areillustrated graphically in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given,with reference to the drawing, of a formation and suitable apparatus forcarrying out the steps of the present method. However, other formations,and arrangements of apparatus, may be employed in carrying out thesesteps. In illustration, there is shown a subterranean carbonaceousformation 11 which serves as a reservoir for formation fluid containingcombustible hydrocarbons desired to be recovered. The formation 11resides below the earths surface 12 covered by an overburden 13 andsupported by strata 14. For present purposes, the overburden 13 andstrata 14 can be considered without carbonaceous matter capable ofsupporting combustion. The formation 11 is of a suitable characterwherein forward in situ combustion can be carried out for the recoveringof hydrocarbons. The formation 11 may be, in example, the heavyoil-bearing sands of California in which forward in situ combustion hasbeen used for recovering hydrocarbons.

The formation 11 is penetrated by spaced-apart injection and productionwells 16 and 17, respectively. The wells 16 and 17 are of suitableconstruction for carrying out a procedure of forward in situ combustionfor recovering hydrocarbons from the formation 11. For example, the well16 has a casing 18 which extends from the earth's surface 12 down intothe lower portions of the formation 11. Openings 19 in the lowerportions of the casing 18 provide a fluid-entry to the surroundingformation 11. The bottom of the casing 18 is sealed by a casing shoe 21.A wellhead 22 encloses the top of the casing 18. A tubing 23 extendsthrough the wellhead 22 downward to adjacent the lower extremity of thecasing 18 and provides for conveying fluids between the earths surface12 and the lower portion of the surrounding formation 11. An additionalfluid connection to the well 16 is provided by port 24 to permit theflow of fluids between the earths surface 12 and the annulus formedbetween the tubing 23 and the casing 18.

The production well 17, for example, has a casing 26 which extends fromthe earths surface 12 down to the lower horizon of the formation 11. Thebottom of the casing 26 is enclosed by a casing shoe 27. Openings 28 inthe lower extremity of the casing 26 provide a fluid-entry to a lowerhorizon of the surrounding formation 11. A wellhead 29 encloses the topof the casing 26. A production tubing 31 extends from the earths surfacedownward to the lower extremity of the casing 26 and terminates adjacentthe openings 28. Fluids produced into the production well 17 arerecovered, via the tubing 31, and sent to a suitablehydrocarbon-recovery facility at the earths surface 12.

The production well 17 has a segregated fluid entry to an upper horizonof the surrounding formation 11. More particularly, a packer 32 isplaced in the casing 26 below the upper horizon and divides theproduction well 17 into two discrete fluid-handling areas. The lowerarea serves for the collection of produced fluids into the productionwell from the lower horizon of the formation 11. The upper area servesfor the passing water, at the upper horizon, from the production well 17into the surrounding formation. For this purpose, openings 33 areprovided in the casing 26 above the packer 32. A fluid connection to theproduction well 17 is provided a port 34 into the casing 26 so thatwater can be passed from the earths surface 12 through the openings 33into the upper horizon of the surrounding formation 11.

The production well 17 carries structures for monitoring the temperatureof the produced fluids as they flow through the production well 17. Suchtemperature-monitoring function can be provided by any suitableapparatus. For example, the production well 17 has a thermocouple Well36 which extends through the wellhead 29 downward to adjacent the lowerextremity of the casing 26. A thermocouple assembly 36a, within thethermocouple well 36 provides for the measurement of temperature atvarious positions within the production well 17. The output from thethermocouple assembly 36a is applied to a temperature-indicating device37. Preferably, the temperature-indicating device 37, of suitabledesign, permits automation of flow control functions.

Forward in situ combustion for recovering hydrocarbons from theformation 11 may now be undertaken. For this purpose, combustiblematerial in the formation 11 adjacent the injection Well 16 is ignited.Also, an oxygen-containing gas is passed through the injection well 16,via the openings 19, to traverse the formation 11 and then to beproduced, via openings 28, into the production well 17. Theoxygen-containing gas will usually be air. However, any other fluidsubstance, which contains sufficient oxidant for carrying out in situcombustion, may be used. In many instances, the flow of air through theformation 11 will cause ignition of the carbonaceous materials thereinby auto-oxidation. However, the combustible matter may be heated toignition by a source of heat applied through the injection well 16. Forexample, an electrical heater may be energized in the well 16 adjacentthe openings 19. The continued injection of air after the combustiblematerial in the formation 11 has been ignited creates a combustion front38 which moves through the formation 11 toward the production well 17.The combustion front 38 is illustrated in the drawing as having movedclosely adjacent the production well 17. The combustion front 38, in itstraverse of the formation 11, produces a burned-out or swept area 39from which formation fluid has been displaced. The heated fluidsgenerated by the combustion front 38, and the formation fluid whichcontains the combustible hydrocarbons desired to be recovered, aredisplaced to and produced through the openings 28 into the productionwell 17. These fluids are removed from the production well 17 throughthe tubing 31. The heated fluids produced into the production well 17from the combustion front 38 can cause temperatures to increase rapidlyin the production well 17. Obviously, after a period of time, increasedtemperatures occur within the production well 17 suflicient that theproduced hydrocarbons are subject to coking and even to being completelythermally destroyed. Cooling must be provided for these produced heatedfluids to avoid this undesired result.

At the time when the temperatures increase undesirably in the productionwell 17, the following steps of the present invention are practiced.Water is introduced through the port 34 under suflicient pressure toflow downwardly through the well 17 and then to be forced, via theopenings 33 in the casing 26, into the surrounding formation 11 at theupper horizon. More particularly, the water is injected at a sufficientrate to form an annular body of water about the production well 17. Withthe injection of water, fluid is produced from the lower horizon of thesurrounding formation 11 through the openings 28 into the productionwell 17. This produced fluid is removed to the earths surface 12 throughthe tubing 31. This fluid is produced through the openings 28 from thesurrounding formation 11 at the lower horizon until the injected waterfrom the openings 33 has flowed coaxially downwardly about theproduction well 17. Stated in another manner, this fluid is producedthrough the openings 28 until the annular body of water about theproduction well 17 has expanded coaxially downward to extend in thesurrounding formation 11 between the upper and lower horizons. As aresult,'there is formed a body of water 41 surrounding the productionwell 17. The body of water 41 is interposed between the production well17 and the advancing combustion front 38 at a horizon intermediate thementioned upper and lower horizons.

The heated fluids from the combustion front 38 must pass into theinjected water, forming the body of water 41, then be coproduced throughthe openings 28 into' the production well 17, and subsequently removedthrough the tubing 31. The injected water 'cools these heated fluids ontheir mixing in the formation 11 The degree of such cooling effectdepends upon the magnitude of flow of injected water passed through theformation 11 from the openings 33. It will be noted that, during thiscooling function, a lower part of the body of water 41'may be convertedinto steam. The steam, in the body 'of water 41, is designated by thenumeral 41'.

The injected water passed from the openings 33 downward along the well17 toward the openings 28 is: controlled in rate of flow so that thewater which enters the production well 17, via the openings 28, issufficient in amounts to maintain therein a temperature between about160 F. and the coking temperature of the hydrocarbons being produced.For this purpose, the temperature-sensing mechanism in the thermocouplewell 36 and the temperature-indicating device 37 are employed to monitorthe temperatures within the production'well 17. Preferably, thetemperature-indicating device 37 is employed by automation to controlthe rate of flow of water into the port 34 for injection'through theopenings 33 into the surrounding formation 11. Such arrangements areconventional and will not be included in the present description.

In some instances, it is of advantage that the water, flowing into theopenings 28, be at least in part steam. Steam flowing in the lowerportion of the production well 17 assists in maintaining well apparatusclear of carbon residues carried therein by the heated fluids which aregenerated by the combustion front 38. Additionally, the steam providesan inert atmosphere within the production well 17 so that explosivemixtures, and possible explosion thereof, cannot occur.

Preferably, the temperature maintained within the production well 17 isbetween the steam-equilibrium temperature under downhole conditions inthe production well 17, and the coking temperature of the desiredhydrocarbons being produced thereinto. This insures a flow'of steam inthe production well 17 at all times.

The advantages of providing, by the aforedescribed steps, a flow ofwater through the formation 11 to produce the body of water 41surrounding the production well 17 will be apparent from the drawing.All heated fluids generated by the combustion front 38 must comminglewith water in the body of water 41 before they can enter into theopenings 28 and be produced from the production well 17. Thus, theportion of the formation 11 which surrounds the production well 17serves as a heat exchanger. Therefore, an inadvertent temporary changeof condition controlling cooling of these heated fluids in thisparticular formation area merely converts more or less of the water, inthe body of water 41, into steam. Additionally, any extreme temperatureswhich result from a reduction in cooling, downstream of the adjacentcombustion front 38, arise in a portion of the formation 11 whichcontains Water. Thus, the only damage that can be expected to occurwould be that to the formation 11 at such high-temperature area and notthe production well 17. Thus, the operability of the production well 17is preserved, and the produced hydrocarbons which flow through thetubing 31 are conserved against thermal injury or destruction.

The'combustion front 38 has a tendency to move vertically upwardly inits movement toward the production well 17. The downward flow of waterabout the production well 17 causes the combustion front 38 to movetoward the lower horizon of the formation 11. Obviously, this increasesthe vertical sweep efliciency of the combustion front 381 and improveshydrocarbon recovery.

As mentioned, the displaced formation fluid which contains thecombustible hydrocarbons is coproduced with the other described fluidsfrom the lower horizon of the formation 11 through the openings 28 intothe production well 17. Thence, these fluids are removed to the earthssurface 12 through the tubing 31. Thereafter, hydrocarbons are recoveredfrom these produced fluids by any suitable means, many forms of whichare known to those skilled in the art.

From the foregoing, it will be apparent that there has been provided amethod employing in situ combustion for recovering hydrocarbons from asubterranean formation including improvements in steps for cooling aproduction well which is subject to being heated to elevatedtemperatures. Various changes and adaptations may be made to the presentmethod by a person skilled in the art without departing from the spiritof this invention. It is intended that the foregoing description beconsidered as illustrative of the present invention whose scope isdefined by the appended claims.

What is claimed is:

1. In a method for recovering hydrocarbons from a subterraneancarbonaceous formation wherein combustion of combustible material in theformation has been initiated and is maintained by injection ofoxygen-containing gas into the formation through an injection wellwhereby there results an in situ combustion front which moves towards aspaced production well, and movement of this front displaces heatedfluids produced by the front and formation fluid containing combustiblehydrocarbons into the production well, and then hydrocarbons arerecovered from these fluids, the'improvement which comprises the stepsof;

(a) passing water from the production well into the surroundingformation at an upper horizon, then downward through the formation aboutthe production well to a lower horizon, and then back into theproduction well from the surrounding formation at the lower horizon, thehorizon at which the combustion front approaches the production wellbeing intermediate the upper and lower horizons,

(b) controlling the rate of water flow so that the water enters theproduction well in amounts sufficient to maintain therein a temperaturebetween about F. and the coking temperature of the hydrocarbons at atime when-the combustion front is sufliciently close to the productionwell to cause increased tem peratures in the production well, and

(c) producing the displaced formation fluid, heated fluids from thecombustion front, and the water, from the lower horizon of thesurrounding formation via the production well, and recoveringhydrocarbons from the produced fluids.

2. The method of claim 1 wherein the rate of water flow is controlled tomaintain the water entering said production well at least in part assteam.

3. The method of claim 1 wherein the rate of water flow is controlled tomaintain the water entering the production well at a rate sufficient tomaintain therein, at downhole conditions, a temperature between thesteamwater equilibrium temperature and the coking tempera ture of thehydrocarbons flowing through the production well.

4. In a method for recovering hydrocarbons from a subterraneancarbonaceous formation wherein combustion of combustible material in theformation has been initiated and is maintained by injection ofoxygen-containing gas into the formation through an injection wellwhereby there results an in situ combustion front which moves towards aspaced production well, and movement of this front displaces heatedfluids produced by the front and formation fluid containing combustiblehydrocarbons into the production well, and then hydrocarbons arerecovered from these fluids, the improvement which comprises the stepsof;

(a) injecting water, at an upper horizon, from the production well intothe surrounding formation to form an annular body of water about thewell,

(b) producing fluid including injected water at a lower horizon, via theproduction well, from the surrounding formation until the body ofinjected water has expanded coaxially downward about the production wellto extend between the upper and lower horizons, said upper and lowerhorizons residing above and below the horizon at which the combustionfront approaches the production well,

(c) injecting the water from the production well into the surroundingformation at the upper horizon at a suflicient rate that the injectedwater produced from the lower horizon of the formation into theproduction well is adequate in amount to maintain the temperature withinthe production well between a temperature where the water is at least inpart steam and the temperature where the desired hydrocarbons aresubject to coking at a time when the combustion front is suflicientlyclose to the production well that the heated fluids from the front cancause thermal destruction of hydrocarbons therein when no injected wateris present, and

(d) producing the displaced formation fluid, heated fluids from thecombustion front, and injected water, from the surrounding formation atthe lower horizon via the production well, and recovering hydrocarbonsfrom said produced fluids.

5. In a method for recovering hydrocarbons from a subterraneancarbonaceous formation wherein combustion of combustible material in theformation has been initiated and is maintained by injection ofoxygen-containing gas into the formation through an injection wellwhereby there results an in situ combustion front which moves towards aspaced production well, and movement o STEPHEN of this front displacesheated fluids produced by the front and formation fluid containingcombustible hydrocarbons into the production well, and then hydrocarbonsare recovered from these fluids, the improvement which comprises thesteps of;

(a) injecting water into the formation surrounding the production wellat a first horizon,

(b) producing said injected water from the surrounding formation at asecond horizon, via the production well, until the injected water flowscoaxially downward about the production well to extend between the firstand second horizons, said first and second horizons residing above andbelow the horizon at which the combustion front initially approaches theproduction well,

(c) controlling the flow of water injected into the formation to anamount such that the injected water produced into the production wellmaintains the temperature within the production well between about 160F. and the temperature at which substantial thermal destruction of thedesired hydrocarbons occurs at a time when the combustion front issuflicently close to the production well that the heated fluids from thefront can produce thermal destruction of hydrocarbons therein, and

(d) producing the displaced formation fluid, heated fluids from saidcombustion front, and said injected water, into said production wellfrom the surrounding formation at said second horizon and recoveringhydrocarbons from said produced fluids.

References Cited UNITED STATES PATENTS J. NOVOSAD, Primary Examiner.

